Stable suspensions of biomass comprising inorganic particulates

ABSTRACT

Liquid suspensions are disclosed comprising a suspending medium, small particles of biomass, and small particles of an inorganic material. The inorganic material stabilizes the suspension, so that it may be transported by pipeline or tank car without developing a sediment. 
     The suspension may be used in manufacturing a bio-fuel.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of International Application No.PCT/EP 2007/058466 filed on Aug. 15, 2007, which was published under PCTArticle 21(2) in English, the contents of which are incorporated hereinby reference, in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

An important aspect of the economics of the use of biomass as a sourceof fuel or of specialty chemicals is the cost involved in transportingthe biomass from the location where it is produced to the location whereconversion to a fuel or to specialty chemicals takes place. It isdesirable to provide a process for converting biomass at or near theplace of production into a pumpable liquid so it may be transported intank cars or a pipe-line.

The present invention provides a liquid composition of biomass suspendedin a liquid suspension medium, further comprising small particles of aninorganic material.

Of particular importance is that these suspensions are stable, meaningthat the solid and liquid phases do not separate within the time neededto store and transport the suspensions (for example via pipe-line, rail,or road transport) to a location where they can be further processed.

It is known from the paper industry to make suspensions of cellulosefibers and inorganic materials. These suspensions do not need to bestable. To the contrary, the cellulose fibers are precipitated from thesuspension and need to make inter-fiber hydrogen bonds (also referred toas paper-making bonds).

It is known from GB 2 310 865 to mix a slurry of biomass material withcatalytic particles and to subject the resulting slurry to pyrolyticconditions. The slurry is processed immediately following itspreparation, so there is no need for the slurry to be stable.

The composition of the present invention may be transported, for exampleby pipeline, or in a tank car or tank truck. The composition may also bestored in tanks. The composition is particularly suitable for use inprocesses whereby the biomass material is converted to liquid or gaseousfuels and/or to the valuable specialty chemicals.

In a specific embodiment the inorganic particulates also possess acatalytic functionality, meaning that the subsequent conversion of thebiomass may be performed under milder conditions (lower temperatureand/or lower pressure and/or shorter time) than was heretofore the case,resulting in improved products and superior process economics.

In a specific embodiment, the biomass comprises polymeric material. Morespecifically, the polymeric material comprises cellulose orlignocellulose. In a preferred embodiment the polymeric materialcomprises both cellulose and lignocellulose.

2. Description of the Related Art

Biomass is produced in large volumes in agriculture and forestry. Manyof these materials are intended for use as food products for humanconsumption, in animal feed, or other forms of valuable materials. Forexample, forestry products are used as construction materials in theform of lumber, plywood, paper and paper products and paper byproductsand the like.

Incidental to the production of agricultural and forestry products, theworld produces vast quantities of agricultural and forestry waste.Examples include wood chips, saw dust, straw, corn husks, bagasse, andthe like. Attempts have been made to convert these waste materials touseful products. In general, these waste materials are converted toproducts of low intrinsic value, such as compost.

Attempts to convert these materials to products of a higher value havemet with limited success. For example, conversion of agricultural wasteto ethanol by fermentation is a time-consuming and expensive process.Moreover, even the most sophisticated fermentation enzymes are only ableto convert at most about 50 percent of the available material. Theremaining 50 percent is immune to attack by fermentation enzymes and issometimes referred to as “recalcitrant cellulose” for this reason.

An alternative to the above approach involves converting the biomass atthe location where it is produced (plantation etc) into a liquid (viapyrolysis or hydrothermal upgrading) or a gas stream (gasification) andto process these streams further in an oil or bio refinery, makingoptimal use of the economy of scale.

Unfortunately, transporting gas is a difficult and costly task, whilemost of the bio-liquids produced from biomass via thermal means areinstable, in the sense that they deteriorate over time in terms ofviscosity and/or chemical composition.

It is therefore an object of the present invention to provide a newliquid composition that can be made from agricultural or forestryproducts, or waste materials from agriculture and forestry, and that issufficiently stable for transportation to a centralized processinglocation. It is a further object of the present invention to provide abiomass composition that is more easily converted to liquid or gaseousfuel or to specialty chemicals than the biomass materials from which itis derived.

BRIEF SUMMARY OF THE INVENTION

The present invention relates to a liquid composition comprising aliquid suspension medium having suspended therein small particles of abiomass material and small particles of an inorganic material, saidcomposition being stable.

These liquid compositions are stable in the sense that the solid andliquid phases do not separate within the time necessary to store andtransport them (via pipe-line or road transport) to a location wherethey can be further processed.

The inorganic material may be inert, for example a salt of an alkalimetal or earth alkaline metal. In an alternate embodiment, the inorganicmaterial may have catalytic activity. Examples include clays, silicas,silica aluminas, zeolites, anionic clays, cationic layered materials,metal hydroxyl salts and the like.

In a specific embodiment, the biomass comprises polymeric material. Morespecifically, the polymeric material comprises cellulose and/orlignocellulose.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The present invention relates to a stable liquid composition comprisingbiomass particles. The liquid composition may be produced at thelocation where biomass is harvested or where it is produced as abyproduct of, for example an agricultural process. The liquidcompositions of the present invention are sufficiently stable to allowthem to be transported to a processing plant where they may be subjectedto further processing.

The liquid compositions of the present invention comprises a liquidsuspension medium having suspended therein small particles of a biomassmaterial and small particles of an inorganic material. Although thesecompositions require the transportation of the liquid suspension mediumand of the particles of an organic material, the pumpability of thesecompositions improves the economics of transportation in such a way thatit more than offsets the additional costs of transporting the liquidsuspension medium and the inorganic material.

The liquid suspension medium preferably comprises water, an alcohol, ora carboxylic acid. For reasons of costs and availability, water-basedliquid suspension mediums are preferred. Alcohol and carboxylic acid maybe added to an aqueous liquid suspension medium so as to change itsproperties. Preferred alcohols for use herein include glycols, inparticular ethylene glycol.

Before incorporation into the liquid composition, the biomass materialis reduced to a particle size preferably in the range of from 3 mm to 50micrometers, more preferably from 1 mm to 0.1 mm. Any suitable methodmay be used for reducing the particle size of the biomass material. Theselection of the method will depend in part on the nature and hardnessof the biomass material, the availability of specific forms of energy atthe location where the biomass is produced or harvested, the desiredparticle size, and the like.

Suspensions of small particles of biomass material in a liquid tosuspension medium tend to be unstable. Biomass particles may eithersettle to the bottom of such a suspension, or float to the surface,whereby a biomass-rich phase is created. As many biomass materials arerich in cellulose, the biomass-rich phase may solidify as a result ofhydrogen bonding between the biomass particles. The mechanism of thisprocess is not unlike that of papermaking from a suspension of cellulosefibers. Once solidified, the biomass cannot readily be brought back intosuspension by agitation. In addition, biomass particles in the presenceof water are subject to microbial deterioration.

It is therefore desirable to provide a way of increasing both thephysical stability and the microbial stability of a liquid compositioncomprising biomass particles suspended in a liquid suspension medium. Ithas now been discovered that the presence of small particles of aninorganic material in such a liquid composition improves both thephysical stability and the microbial stability of the composition.

The physical stability of the liquid composition may be determined bythe following standardized stability test. A centrifuge tube is filledwith the appropriate amount of suspension, as described in the manual ofthe equipment. The tube is closed with a stopper and the suspension iscentrifuged for 10 min at 5000 rpm. Immediately after centrifuging, thetube is removed from the centrifuge and slowly turned upside down andback (5 times). Then the content of the tube is carefully emptied. Thetube is visually examined for the presence of a layer of solid materialleft on the bottom. If no solid material is present on the bottom of thetube the suspension is considered to be stable. Therefore, the term“stable” as used herein is made with reference to this centrifuge test.

Even if the presence of the inorganic particles may not sufficientlyimprove the physical stability of the suspension, the coating ofinorganic material onto the biomass particles may decrease the amount ofhydrogen bonding that takes place between biomass particles. As aresult, a suspension that has undergone phase separation may be restoredby simple agitation.

The stability of the suspension may be further improved by the additionof an anti-flocculant. Anti-flocculants are charged materials thatattach to the surface of a suspended particle. As a result thezeta-potential of the particle is increased, which reduces theprobability of coagulation or agglomeration with other particles in thesuspension. In general, any multivalent soluble ion is suitable as ananti-flocculant. Pyrophosphate is a suitable example.

An alternate method for further improving the stability of thesuspension comprises the use of a surfactant material. Surfactantmaterials are often considered a special form of anti-flocculants, buttheir mechanism of action is different. Surfactant molecules arecharacterized by a polar head and a non-polar tail. The polar head maybe ionic or non-ionic. The polar head will attach to the surface of asuspended particle, with the non-polar tail sticking out into thesolvent. As a result the particle becomes hydrophobic. Preferred arelow-cost surfactants, such as soaps.

Swelling agents promote the absorption of solvent molecules into thesuspended particles. As a result of the swelling, the density of thesuspended particle becomes closer to the density of the solvent, therebyreducing the tendency of the particles to settle or to float to thesurface. Suitable swelling agents include acids and bases. The choice ofswelling agent will depend on the nature of the inorganic particles, forcompatibility reasons.

In a preferred embodiment, the biomass material comprises a polymericmaterial, more preferably cellulose and/or lignocellulose. Morepreferred are biomass materials that contain both cellulose andlignocellulose.

The inorganic material preferably is in crystalline or quasi-crystallineform. The purpose of the present invention may be achieved with aninorganic material that is an inert inorganic material. The term “inert”as used herein refers to materials that do not have a catalytic effecton a conversion reaction (such as pyrolysis or hydrothermal treatment)to which the composition may be subjected.

It is, however, desirable to use inorganic material that has catalyticproperties in a subsequent conversion reaction. Examples of suchmaterials include clays, silicas, silica aluminas, transition metalhydroxides, metal hydroxyl salts, zeolites, cationic layered materials,anionic clays, layered double hydroxides (LDHs), smectite clays,saponites, sepiolites, and mixtures thereof.

The present invention further provides a method for preparing a liquidcomposition of biomass suspended in a liquid suspension medium, saidcomposition being stabilized by small particles of an inorganicmaterial, said method comprising the steps of:

-   a. contacting particles of the biomass with the liquid suspension    medium having dissolved therein precursor material to the inorganic    particles in;-   b. allowing the solution to coat and/or penetrate the polymeric    material;-   c. modifying the conditions to cause the formation of an inorganic    particulate material from the precursor material.

Step c. may involve changing the pH, changing the temperature,evaporating part of the liquid suspension medium, changing the ionicstrength, etc.

Preferably, the liquid suspension medium comprises water, and mayfurther comprise an alcohol and/or a carboxylic acid. The liquidsuspension medium may further comprise a swelling agent, for example aBronstedt acid or a Bronstedt base. Suitable acids include mineralacids, such as hydrochloric acid, sulfuric acid, and phosphoric acid.Suitable bases include the hydroxides and carbonates of the alkali andearth alkaline metals. If the liquid suspension medium comprises acarboxylic acid, the swelling agent preferably is also an acid.

The biomass material preferably comprises a polymeric material, morepreferably cellulose and or lignocellulose. The inorganic material ispreferably in crystalline or quasi crystalline form.

In a specifically preferred embodiment, the biomass comprises celluloseand the inorganic material is a hydrotalcite like material. Thehydrotalcite like material may conveniently be formed in situ.Accordingly, the present invention provides a method for preparing acellulose-containing polymeric liquid suspension comprising smallparticles of an inorganic material, said method comprising the steps of:

a. providing a cellulose-containing polymeric material;

b. providing an aqueous solution of a divalent metal and a trivalentmetal;

c. soaking the cellulose polymeric material with the aqueous solution;

d. initiating the formation of a microcrystalline inorganic material.

The preferred hydrotalcite like material is hydrotalcite itself.Accordingly, the preferred divalent metal in step b. is magnesium, andthe preferred trivalent metal is aluminum. The microcrystallineinorganic material formed in step d. is preferably an anionic clay, andmost preferably hydrotalcite.

In yet another embodiment the inorganic material is an inorganic oxide,such as alumina. Accordingly, the present invention provides a methodfor preparing a cellulose-containing polymeric liquid suspensioncomprising small particles of an inorganic material, said methodcomprising the steps of:

-   a. providing a cellulose-containing polymeric material, such as    biomass;-   b. providing an aqueous solution of a cation or anion of a metal    capable of forming a particulate inorganic compound;-   c. soaking the cellulose polymeric material with the aqueous    solution;-   d. initiating the formation of a precursor to a particulate    inorganic compound;-   e. aging to convert the precursor to the particulate inorganic    compound.

In this embodiment, a preferred cation for use in step b. is Al³⁺, and apreferred anion is aluminate (Al₂O₄ ²⁻).

The liquid composition of the present invention may be used to produce avariety of useful materials. For example, it may be used in thepreparation of a bio-oil, it may be converted to a binder material, orto a construction material.

The liquid composition may be transported by pipeline or road transportor rail transport to a central processing location. Further, the liquidcomposition may be used as a feedstock in processes whereby the biomassmaterial is converted to liquid or gaseous fuels and/or to valuablespecialty chemicals.

Examples of such a process include one of a variety of processes presentin a traditional oil refinery, such as gasification, steam reforming,thermal cracking, coking, catalytic cracking, hydro-cracking, andhydro-processing. The inorganic material may be selected such that itfunctions as a catalyst in any of these processes.

The liquid composition of the present invention may be used as afeedstock in a fluid catalytic cracking unit. For this purpose, thecracking catalyst in the unit should have a low cracking activity,because biomass materials are much more prone to cracking than thetraditional feedstocks derived from crude oil. For this reason, it maybe desirable to feed the liquid composition into a low cracking activityzone of a fluid catalytic cracking unit. Examples of such low activityzones include the stripper and the regenerator of a traditional FCCunit.

What is claimed is:
 1. A liquid composition comprising a water-basedliquid suspension medium having suspended therein particles of a biomassmaterial and particles of an inert inorganic material, wherein thebiomass material has an average particle size in the range of 3 mm to 50micrometers, wherein the inorganic material has an average particle sizein the range of 3 mm to 50 micrometers, wherein said suspension does notprecipitate solid particles when centrifuged for 10 minutes at 5000 rpm.2. The composition of claim 1 wherein the inorganic material is incrystalline or quasi-crystalline form.
 3. The composition of claim 1,wherein the biomass material comprises a polymeric material.
 4. Thecomposition of claim 3, wherein the polymeric material comprisescellulose and lignocellulose.
 5. The composition of claim 1 wherein theparticles of biomass material have an average particle size in the rangeof from 1 mm to 0.1 mm, wherein the particles of inorganic material havean average particle size in the range of from 1 mm to 0.1 mm.
 6. Thecomposition of claim 1, wherein said composition is converted to bio-oilunder mild conditions.
 7. The composition of claim 1 which istransported by pipe-line or road transport to a central processinglocation.
 8. The composition of claim 1 which is used as a feedstock ina process whereby the biomass material is converted to liquid or gaseousfuels and/or to chemicals.
 9. The composition of claim 8 whereby theprocess is an oil refinery process selected from the group consisting ofGasification, Steam reforming, Thermal Cracking, Coking, CatalyticCracking, Hydrocracking, and Hydro-processing.
 10. The composition ofclaim 9, whereby the process is a Fluid Catalytic Cracking process witha low cracking activity catalyst.
 11. The composition of claim 10,whereby the suspension is fed into a low cracking activity zone of theFluid Catalytic Cracking process, wherein said low cracking activityzone comprises a stripper or regenerator.
 12. The composition of claim1, wherein said composition further comprises an anti-flocculant. 13.The composition of claim 1, wherein said composition further comprises asurfactant material.
 14. The composition of claim 1, wherein saidcomposition further comprises a swelling agent.
 15. The composition ofclaim 1, wherein said inorganic material comprises an alkali metaland/or an earth alkali metal.